1. Field of the Invention
The invention relates to a structure of an inkjet printhead applicable to an image recording apparatus and other apparatuses that record information, image or others on a recording medium by ejecting droplets of ink from nozzles.
2. Description of Related Art
As a conventional inkjet printhead, there is a piezoelectric inkjet printhead disclosed in JP-A-2004-223880 (especially FIG. 2) by the present applicant, for instance. The piezoelectric inkjet printhead includes a cavity unit, a planar piezoelectric actuator, and a flexible flat cable. The cavity unit has a plurality of nozzles, which are arranged in rows in a front surface of the cavity unit, and a plurality of pressure chambers respectively corresponding to the nozzles. The piezoelectric actuator has a plurality of active portions formed for the respectively corresponding pressure chambers. The flexible flat cable is for supplying therethrough electric power to the piezoelectric actuator.
In the cavity unit, there are formed complex ink passages for the respective nozzles. That is, a plurality of common ink chambers each of which is long in a direction in which each row of the nozzles extends, are formed inside the cavity unit, and each of the ink passages extends from one of a plurality of ink supply ports to the nozzle via one of the common ink chambers and one of the pressure chambers. Thus, ink supplied from an ink supply source into the cavity unit via the ink supply port is first introduced into the common ink chamber, and then distributed to all pressure chambers connected to the common ink chamber and disposed on a back surface of the cavity unit. To form such complex ink passages in a cavity unit that is a small component, the cavity unit is formed by stacking a plurality of thin flat plates in each of which through-holes and/or recesses of various sizes are formed.
In the cavity unit disclosed in the above-mentioned publication, a plurality of the ink supply ports open in the back surface at a place near a shorter edge thereof. An ink introducing passage extends from each ink supply port in a direction of stacking of the plates (hereinafter referred to as “the stacking direction”), namely, toward a front side of the cavity unit, and is connected to one of two opposite longitudinal ends of one of the common ink chamber that is formed through plates disposed in the middle of the stack of the plates of the cavity unit. The ink supply ports are covered by a filter member having a filtering portion in order to prevent introduction of foreign material into the cavity unit.
As described above, the cavity unit is constituted by a plurality of plates, and the ink introducing passage extending in the stacking direction is constituted by an ink supply port formed through a cavity plate constituting the back surface of the cavity unit, and two connection openings respectively formed through a base plate and a supply plate interposed between the cavity plate on the back side and two manifold plates through which the common ink chambers are formed. Contours of each ink supply port and the corresponding connection openings are the same and aligned in the vertical direction, so as to form an ink introducing passage extending in the stacking direction. The ink introducing passage is connected to one of two opposite longitudinal end portions of the common ink chamber to form right angles with a bottom surface of the common ink chamber thereat. Thus, the ink introducing passage and the common ink chamber are connected to form an L-shaped connecting portion as seen in the direction perpendicular to the stacking direction and the longitudinal direction of the common ink chamber.
According to the above-described conventional arrangement, when the ink flows into the common ink chamber from the ink introducing passage, the ink flow should turn at a right angle along the L-shaped connecting portion between the ink introducing passage and the common ink chamber. At this place, the ink flows at a higher rate on an internal side of the L-shaped connecting portion than on an external side. Hence, a corner portion on an uppermost stream side of the common ink chamber, which side corresponds to the external side of the L-shaped connecting portion, becomes a dead water region where the ink flow stagnates, and bubbles in the ink tend to be collected and accumulated at this corner portion. Even when it is tried to remove the bubbles by sucking the accumulated bubbles along with the ink, from the side of the nozzles or the side of the ink supply source, it does not work well, since the ink does not easily flow at the corner portion.
Further, when the bubbles accumulated at the corner portion aggregate into a large mass of air in the ink introducing passage, the large air mass is inhibited from moving from the ink supply port to the upstream side by the filter member covering the ink supply port.
Consequently, the ink introducing passage is narrowed by the large air mass, thereby delaying supply of the ink through the filter member into the common ink chamber. This causes shortage in the ink supply into the common ink chamber.
In addition, an air mass having grown to some size at the corner portion may move with the ink flow to close a pressure chamber, thereby causing failure in ejection of an ink droplet from a nozzle.